Method of forming a composite structure comprising a chromecontaining member



p 9, 1952 F. H. MASON METHOD OF FORMING A COMPOSITE STRUCTURE COMPRISING A CHROME-CONTAINING MEMBER Filed Sept. 27, 1947 INVENTOR.

.lllllllll I iatented Sept. 9, 1952 2,609,598 TE STATES ATENT oFFl-CE.j

' METHOD OF FORMING A COMPOSITE STRUCTURE COMPRISING A CHROME- CONTAINING MEMBER' Y I Frederick H. Mason, Detroit, Mich, assignor to Chrysler Corporation, Highland Park, Mich., a corporation of Delaware 7 f Application September 27, 1947, Serial nannies 1 This application relates to a method of joining parts by means of a metallic bond. More specifically, it relates to a bonding process involving applying a preliminary coating to one of a plurality of objects to be joined, which object would be 5 very end of the tube I4. The portion of the tube damaged by the use of flux otherwise required in Hi to the left of the copper-coated side of the the bonding process but for the use of the coating. plate to is expanded, as indicated in Fig. 2, by a The process of this invention may be applied suitable tool, not shown, and so a very smallanto the bonding of parts containing a percentage nular opening H is formed between the nickel of chromium sufficient to form a bond-resisting 10 coating is at the start of the expansion and the oxide upon being heated for bonding. If the edge of the copper plating l2 at the hole l3. aforesaid parts are thin-walled tubes, for exam- Now the plate Ill and tube M are placed in a ple, the flux required to prevent the formation of brazing atm phere and subjected to a braz chromium oxide will eat through the thin tube process involving at least six hours at 1500 F. and walls, unless resort is had, not to the ordinary b v erlde op temperature o 2100" F. The time brazing atmosphere, but to one that is very free and te perature are sufi'icient for the copper coatof oxide-forming components such as oxygen and ing-l2 to melt and to be drawn by capillary action especially moisture and thus is very expensive. t o the annular sp 6 to the clearance The thin-walled tubes may be bonded to other space shown in Figs. 1 and2 between the nickel parts to form a regeherator or heat exchanger for coating l6 an the tube 14' and the plate Opening recovering waste heat from a gas turbine and apl3 and to alloy with th ic e 0f the pl 10 plying it to air going to burners supplying hot and with the nickel coating 16 on the tube l4. gases for the aforesaid gas turbine. The copper-nickel alloy forms a good heat resist- In th drawings: ant bond sufiicient for the purposes to which the Fig; 1 shows a plate and tube positioned in an tube and plate are to be put, as will be described opening i th lat later. The nickel coating is does not completely Fig. 2 shows the plate and tube of Fig. 1 after alloy with the tube 14, but the alloying is suificient th t be has been expanded; to insure good bond between the coating and the Fig. 3 shows the plate and tube after they have tube th y making t pp r-ni kel bond efbeen bonded to one another; and fectively seal the tube [3 to the plate It].

Fig, 4 shows an alternate process for joining If it is not feasible to extend the length of the the tube and plate. present process to six hours above 1500 F. as Reference character [0 designates anickel plate p u y tio d, the tube and its coatin having on one side a chromium coating l l and may be subjected to a suitable heating process on the other side a copper coating I2. The late before assembly of the tube and plate to effect a 10 has an opening l3 in which is positioned a u fi e alloying of the coating a d tube by difchromium-containing tube M, which may have, fusion for a g d joint between the coatin d for example, such compositions as 13% chromium t t Alt r a su a h a p rat n and the balance nickel; 18% chromium, 8% y be Carried on after the brazing has been nickel, a small amount of columbium, and the effected. r I balance iron; and 20% chromium, 65% cobalt, and The bulge l5 may be formed before or after the the balance tungsten and nickel. The coating of coating I6 is applied to the tube M. It will be tube I4 with nickel plating I6 is carried out when convenient to app y o ings l I and I2 to the the surface of the tube is free of oxide and for plate It] before the hole I3 is formed therein. The eign matter and at the plating temperatures invarious coatings ll, l2, and 16 may be applied by volved there is little, if any, tendency for chrothe process f trcdeposition. Special care mium oxide to form from the chromium cont nt, mustbe taken in the case of the nickel coating l6 of the tube. The present improvement, however, on the tube M to insure that all oxides have been is most advantageously carried out when the tube ed from the portion of the tube to be coated. has sufiicient percentage of chromium t form a 60 because any oxide left beneath the coating 16 may bond-resisting oxide on heating subsequently to b ister du g e present process and thereby i plating to the relatively higher temperatures necterfere with the strength of the metallic bond essary for bonding. About 5% chromium is sufiiformed. cient for forming the above bond-resisting oxide. As shown in Fig. 3, some of the copper coating The nickel coatin may be applied to a tube of I2 r mains on h plate In, having alloyed with pure chromium, although it is more advantathe plate, because the present process may involve geously used when the tube contains another an appreciable time above 1500 F., at hi 1. metal permitting the nickel coating to alloy by loying by difiusion takes place at an appreciabl diffusion with the tube more readily than when 0 rate, and below 1960 F., the temperature at which the tube contains only chromium.

2 Claims. (ores-sis).

...The tube Ill-"has an externalcircumferential bulge--15 adjacent the chromium-coated side of the plate In and a nickel coating [6 extending from the bulge l5 extendin perhaps as far as the coppermelts and will runi'nto the space between ed heating'and brazing process also causes the chromium coating 1 I to alloy by diffusion to some extent with the nickel plate H1.

The nickel coating l6 has been applied to thetube M as a preliminary step to the present oper ation, because the relatively high chromium content of the tube [4 would cause the present heat to produce bond-resisting chromium Oxide on the tube M, which could be avoided only with the use of a very expensive atmosphere that is free of oxygen-forming impurities, particularly moisture or by the use of a fiux which has a tendency to eat through the wall of the tube M, which in a desired example is only about .005? in thickness. When the thickness of the tube 16' is about .005" as above mentioned, thenick'el coating It may" be .003" to .005, the copper coating i2, .015, and the chromium coating H, .002. The difference in diameter between the coated portion of the tube 14 and the hole :3'may vary from .001" to .01". In any'event, the tight fit employed between steel parts about to be brazed with copper is not used with the nickel-coated tube hi and the nickel plate 10, because copper flows less readily on nickel than on steel.

In the alternate process of Fig. 4 the end of the tube [4 is left unexpanded and a copper ring I! is substituted for the copper coating 12. When the parts of Fig. 4 are-heated, the-copper ring I! is melted and drawn into the space between plate opening 13' and thet ubeooating l6 and alloys therewith, as previously described, with respect to Figs. 1, 2, and-3'. The advantage of the construction' of Fig. 3 is'that the expanded portions of the tube 14' at both sides of the plate 10 relieve the copper-niokel'bond of stresses due-to limited longitudinal movement of the tube with respect to the plate;

Broadly'speaking, the nickel coating H5 is applied to the tube- M", because the tube contains chromium in a percentage sufiicient' to form a bond-resisting oxide, which is about 5%; No coating need beapplied to the hole 13 in the plate 10, becausethe plate contains less than the 5% chromium leading to the formation of the bond-resisting'oxide; and. in actual fact, no chromiurn;

The'joint' construction described with reference toFigs; 1 to 4"inclusive, may be used in a regenerator-or heat exchanger for recovering waste heat from the exhaust to the gas turbineand applying the waste heat to air fed to burners supplying gases for the gas turbine. In the regenerator the plate l0 may be a bulk head or sheet to which a plurality of parallel tubes l4 arebonded and attached, and there is a bulk head on each end of the tubes. Hot gases coming from the turbine come into contact with the exterior of the tubes l'between the plates or bulkheads l0 and air on its wayto the burners supplying'the'turbine is fed through'the tubes I4. The chromiuin'coating l i on the plate It] provides good resistance to the hot gases coming from the turbine, especially if they contain sulphur.

I claim I 1. A method of bonding comprising providing a nickel plate having a holeand a coating of copper on oneside around the hole'and a tube containing nickel and chromium with an external bulge greater in external diameter than the hole'in the plateand spaced from oneend of the tube a distancegreater than thethickn'essof the plate and an ex'temal coating ofnickel extendingfrom the bulge toward the said one end of the tube, placing 4 the tube in the hole in the plate so as to make a portion of the tube adjacent the said one end thereof to extend beyond the copper-coated side of the plate, the tube bulge and the other side of the plate to be juxtaposed, and the plate hole directly to surround a nickle-coated region of the tube, expanding the said tube portion beyond the copper-coated side of the plate to make the outer diameter of the said tube portion greater than the diameter of the plate hole and the said tube portion to" form with the copper-coated side of the plate a very small annular opening leading to the space between the plate hole and the nickel coating on the tube, heating the plate and the tube to a temperature above 1500 F. at which the nickel coating on the tube alloyswith the tube, and maintaining at a temperature above 1500" for a su'fiicient time for the nickel coating on the tube to alloy with the chromium-containing tubew'ithoutthe chromium penetrating through the nickel coating in substantial quantities to the external surface of the latter and at a temperature up to 2100 F. to cause the copper coating on the plate to be drawn through the aforesaid annular opening and to alloy with the plate hole and the nickel coating on the tube.

2. A method of bonding a first part having a surface containing nickel and mor than about 5% chromium to a secondpart'havinga surface containing nickel and less than about 5% chromium, said method comprising coating the surface of the first part with nickel, juxtaposing the parts so as to bring the surface of the second part in closely spaced relation to the nickel coating on'the surface of the first part, applying heat to the juxtaposed parts in the presence of a' copper bonding metal for the ultimate bonding of the same together, to a temperature above 1500. F. at which the nickel coating alloys with the first part, and maintaining the parts at a temperature above 1500 F. for a sufficient time for the nickel coating on the first part to alloy with the chromium-containing first part without the chromium thereof penetrating through the nickel coating in substantial quantities to the external surface of the latter andat a temperatore up to 2100 F. for causing the copper metal to melt in order to flo between the nickel coating and the surface on the second member and therewith FREDERICK H. MASON.

REFERENCES CITED Thefollowing references are of record in the file of this patent:

UNITED STATES PA'I'ENTS Number Name Date' 1,250,881 Hodges Dec. 18, 1917 1,804,237 Steenstrup May 5, 1931 2,117,106 Silliman May 10,- 1938 2,123,384 Silliman July 12, 1938 2,197,039 -Gottlieb Apr. 16, 1940 2,269,523 Deutsch Jan. 13, 1942 2,364,109 Taylor -Dec. 5, 1944 2,390,452 Mudge 'Dec. 4, 1945 2,446,890 Gilbertson -Apr. 12, 1949 FOREIGN PATENTS Number Country Date 309,032 Great Britain Oct. 24, 1929 547,755 Great Britain Sept. 2, 194

OTHER REFERENCES Steel Mag, July 21, 1947, FurnaceBrazing, pp. 103, 104, 106, 124 and 127.

Methods for Placing Brazing Materials, and Vent Locations, Prod. Eng, July 1947, p. 127. 

2. A METHOD OF BONDING A FIRST PART HAVING A SURFACE CONTAINING NICKEL AND MORE THAN ABOUT 5% CHROMIUM TO A SECOND PART HAVING A SURFACE CONTAINING NICKEL AND LESS THAN ABOUT 5% CHROMIUM, SAID METHOD COMPRISING COATING THE SURFACE OF THE FIRST PART WITH NICKEL, JUXTAPOSING THE PARTS SO AS TO BRING THE SURFACE OF THE SECOND PART IN CLOSELY SPACED RELATION TO THE NICKEL COATING ON THE SURFACE OF THE FIRST PART, APPLYING HEAT TO THE JUXTAPOSED PARTS IN THE PRESENCE OF A COPPER BONDING METAL FOR THE ULTIMATE BONDING OF THE SAME TOGETHER, TO A TEMPERATURE ABOVE 1500* F. AT WHICH THE NICKEL COATING ALLOYS WITH THE FIRST PART, AND MAINTAINING THE PARTS AT A TEMPERATURE ABOVE 1500* F. FOR A SUFFICIENT TIME FOR THE NICKEL COATING ON THE FIRST PART TO ALLOY WITH THE CHROMIUM-CONTAINING FIRST PART WITHOUT THE CHROMIUM THEREOF PENETRATING THROUGH THE NICKEL COATING IN SUBSTANTIAL QUANTITIES TO THE EXTERNAL SURFACE OF THE LATTER AND AT A TEMPERATURE UP TO 2100* F. FOR CAUSING THE COPPER METAL TO MELT IN ORDER TO FLOW BETWEEN THE NICKEL COATING AND THE SURFACE ON THE SECOND MEMBER AND ALLOY THEREWITH. 